#!/usr/bin/perl

use strict;
use warnings; 

my %myhash; 
my $var = "qiz";  # <- $var soll global sein!

$myhash{'foo'} = "bar";

foreach $var (keys %myhash) {
    print $var;
    mysub();
}

sub mysub {
    print "$var\n";  # <-- Wieso undef?
}